The present invention relates to a method of cryogenically separating a mixture of atmospheric gases within a distillation column system having one or more columns. More particularly, the present invention relates to such a method in which descending liquid and ascending gaseous phases of the mixture are contacted through the use of structured packing to effect the separation between components of the mixture of atmospheric gases.
Mixtures of atmospheric gases, that is mixtures of gases found in air or air itself, for example, nitrogen, oxygen, argon, and etc. are separated in a variety of cryogenic distillation systems that are optimized for production of desired atmospheric gas components. Typically air as a mixture of atmospheric gases is refined into its various constituents through the use of a cryogenic distillation column system in which the air is first compressed and purified and then is cooled to cryogenic temperatures that are at or near its dew point. The cooled air is introduced into a distillation column in which actual separation takes place. Upon introduction to the distillation column, the higher volatility components, for instance, nitrogen, boil before the lower volatility components such as oxygen to create an ascending gaseous phase. A portion of the ascending gaseous phase is condensed to reflux the column and thereby to originate a descending liquid phase. The descending liquid phase is contacted with the ascending gaseous phase through a variety of well known contacting elements so that the liquid phase becomes more concentrated in the lower volatility components while the ascending gaseous phase becomes ever more concentrated in the higher volatility components.
The distillation column system may include a single column to produce a gaseous nitrogen product or a series of columns to further refine the air and to produce nitrogen, oxygen and argon products. Further columns may be used to further separate and produce other components of the air.
The liquid-gas contacting elements that are used to contact descending liquid and ascending gaseous phases of the mixture can be provided by various packings, trays, plates and etc. Structured packing has become a popular liquid-gas contacting element for cryogenic separations of mixture of atmospheric gases due to be low pressure drop characteristics of such packings. This low pressure drop characteristic can be advantageously realized in lower energy costs, greater production, and etc. The disadvantage of structured packing is its high initial cost as compared with the cost of conventional plates and trays.
A long held belief in the prior art is that the performance of structured packing deteriorates within increased pressure. As will be discussed, the inventors herein have found that the performance of structured packing, can increase with increased pressure when the mixture to be separated is a mixture of atmospheric gases. This fact can be put to use in producing columns of higher capacity using lower volumes of structured packing than have been previously considered. The decrease in volume of the structured packing will decrease the capital expenditures involved in fabricating a distillation column.